Classifications

• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F13/00—Interconnection of, or transfer of information or other signals between, memories, input/output devices or central processing units
  • G06F13/14—Handling requests for interconnection or transfer
  • G06F13/16—Handling requests for interconnection or transfer for access to memory bus
  • G06F13/1605—Handling requests for interconnection or transfer for access to memory bus based on arbitration
  • G06F13/1652—Handling requests for interconnection or transfer for access to memory bus based on arbitration in a multiprocessor architecture
  • G06F13/1663—Access to shared memory
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F13/00—Interconnection of, or transfer of information or other signals between, memories, input/output devices or central processing units
  • G06F13/14—Handling requests for interconnection or transfer
  • G06F13/16—Handling requests for interconnection or transfer for access to memory bus
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F13/00—Interconnection of, or transfer of information or other signals between, memories, input/output devices or central processing units
  • G06F13/14—Handling requests for interconnection or transfer
  • G06F13/16—Handling requests for interconnection or transfer for access to memory bus
  • G06F13/1605—Handling requests for interconnection or transfer for access to memory bus based on arbitration
  • G06F13/1647—Handling requests for interconnection or transfer for access to memory bus based on arbitration with interleaved bank access
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F13/00—Interconnection of, or transfer of information or other signals between, memories, input/output devices or central processing units
  • G06F13/14—Handling requests for interconnection or transfer
  • G06F13/16—Handling requests for interconnection or transfer for access to memory bus
  • G06F13/1605—Handling requests for interconnection or transfer for access to memory bus based on arbitration
  • G06F13/1652—Handling requests for interconnection or transfer for access to memory bus based on arbitration in a multiprocessor architecture
  • G06F13/1657—Access to multiple memories
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L49/00—Packet switching elements
  • H04L49/10—Packet switching elements characterised by the switching fabric construction
  • H04L49/103—Packet switching elements characterised by the switching fabric construction using a shared central buffer; using a shared memory
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L49/00—Packet switching elements
  • H04L49/10—Packet switching elements characterised by the switching fabric construction
  • H04L49/101—Packet switching elements characterised by the switching fabric construction using crossbar or matrix
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L49/00—Packet switching elements
  • H04L49/30—Peripheral units, e.g. input or output ports
  • H04L49/3018—Input queuing
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L49/00—Packet switching elements
  • H04L49/35—Switches specially adapted for specific applications
  • H04L49/351—Switches specially adapted for specific applications for local area network [LAN], e.g. Ethernet switches

Definitions

• the invention relates generally to memory interface systems, and more specifically to a method and apparatus for providing and arbitrating access to a shared memory by multiple devices, for applications such as multiprocessor systems and communications switching.
• Shared memories are used to facilitate data passing between multiple processes.
• a typical shared memory implementation involves the use of multiple ports. Each port may provide shared memory access to a different external device. The different devices, in turn, may be involved with the control or execution of different processes that pass the data.
• the path to the shared memory typically is designed with a bandwidth close to the sum of the bandwidths of the individual ports. This ensures that the data carrying capacity of the path is sufficiently large so that no port suffers a significant delay in accessing the shared memory even though multiple ports may seek access to the shared memory. Generally, this is achieved in one of two ways, or some combination thereof.
• the shared memory access time may be designed to be much faster than the data transfer times for the individual ports.
• the path width to the shared memory may be designed to be much greater than the path widths of the individual ports.
• the first approach is to assign a time slot to each port during which data can be read from or written to the shared memory.
• the assigned time slot is shorter than the actual time required to transfer data through the port.
• the data is buffered temporarily during its transfer between a port and the shared memory.
• the length of the port time slot is inversely proportional to the number of devices sharing access to the shared memory.
• a device using a particular port can gain access to the memory only during the assigned time slot for that port.
• Data is buffered between time slots.
• the second approach also involves assigning a time slot to each port. For example, writes to the shared memory involve temporarily buffering multiple data words received at a respective port, and then providing them to the memory on a wide memory path all in one memory access cycle during the time slot designated for the port. Conversely, reads from the shared memory involve providing multiple words on the wide path all in one memory access cycle during a time slot designated for a respective port; temporarily buffering the words read from memory; and then transferring the words through the port.
• This second approach is particularly well suited to burst-mode systems in which data words are communicated in multi-word bursts through respective ports.
• a complete burst may be temporarily stored in a memory access buffer, and then may be written or read during a single memory access cycle through such a wide bandwidth path to the shared memory.
• each port may be made to appear to have exclusive access to the shared memory, unimpeded by data transfers through other ports.
• the illustrative block diagram of Figure 1 depicts an earlier implementation of a multi-port memory system in which k ports, each having word width m, equally share a common memory. Each burst includes k words. K memory access buffers each can store k m-bit words. Each buffer is connected to the shared memory by a k x m line wide path. The shared memory is k x m bits wide.
• FIG. 2 The illustrative drawings of Figure 2 show a data format used in a typical multiport memory system such as that in Figure 1.
• a k word burst of m-bit words passes through a port.
• the entire burst is briefly stored in a single memory access buffer.
• all k-words of the burst are simultaneously transferred from the buffer and written to the shared memory on the k x m path.
• k words are read from the shared memory during another prescribed time slot and are transferred to a single memory access buffer. Then the buffered data is transferred through the port associated with that buffer.
• the port which originally inputted the burst may be different from the port that outputs the burst.
• the shared memory temporarily stores the burst so that it can be routed from the input port to the output port.
• the system of Figure 1 can be used to pass data between ports. More specifically, for example, in a memory write operation, k m-bit words received through a respective port are buffered by a memory access buffer assigned to that port. Subsequently, during a time slot reserved for that memory access buffer, all of the k m-bit words stored in the assigned buffer are simultaneously written to the shared memory on the shared k x m-bit wide path. In a like manner, each of the other buffers can store m-bit words on behalf of their own associated ports. The entire contents (all k words) of each individual buffer can be written to the shared memory during the individual time slot reserved for that buffer.
• a memory read operation is analogous, with the steps of the write operation reversed.
• FIG. 3 is a block diagram depicting another conventional multi-port shared memory system.
• the data format used involves 16 word bursts of 72 bits per word (64-bit data plus 8-bit parity) .
• the shared memory bus has a width of 1152 lines (16 words x 72 bits/word) .
• the bus is connected to each of 16 memory access buffers.
• Each buffer would need more than 1224 data pins, 1152 to connect to the bus and 72 to connect to the port.
• the 1152 data pins connected to the bus would each require high drive capability to operate on a bus connected to all 16 buffers and to the shared memory.
• Figure 3 shows an illustrative bus capacitance that must be overcome by the buffer pins.
• the architecture should require fewer pins for memory access buffers and should not require high drive capability for buffer pins.
• the present invention meets those needs.
• a novel multi-port memory system includes a random access memory. Multiple buffers are provided for temporarily storing data during transfer of the data between respective ports and the random access memory.
• a data path interconnects the random access memory and the multiple buffers.
• An interconnect circuit conducts different prescribed subsets of data between the ports and different prescribed buffers.
• a port burst is a multi-word burst of data transferred through a single port.
• Data words in respective port bursts are partitioned into multiple subsets. Each data word subset is associated with a temporary storage buffer. Data word subsets are conducted between respective ports and their respective associated buffers where they are temporarily stored. An entire port burst can be transferred between the multiple buffers and the random access memory in a single memory access cycle.
• the present invention reduces the number of pin connections required to transfer a multi-word burst of data between a port and a shared memory. Further, a present embodiment of the invention reduces the output drive requirements of memory access buffers.
• Figure 1 is a block diagram of an earlier multi-port shared memory system
• Figure 2 is a data format which can be used in the earlier system of Figure 1;
• Figure 3 is a block diagram of another earlier multi-port shared memory system
• Figure 4 is a generalized block diagram of a first multi-port shared memory system in accordance with the present invention.
• Figure 5 shows a data format and data flow used in the embodiment of Figure 4.
• Figure 6 is a more detailed block diagram of memory access buffers and control logic of the embodiment of Figure 4;
• Figure 7 is a block diagram of a representative dual register pair of the memory access buffers of Figure 6;
• Figure 8 is a timing diagram which explains the operation of the control logic and memory access buffers of Figure 6;
• Figure 9 is a timing diagram which explains the operation of the dual register pairs of Figure 7; and Figure 10 is a block diagram of an Asynchronous Transfer Mode switch in accordance with the present invention.
• the present invention comprises a novel method and apparatus for implementing a multi-port shared memory system.
• the following description is presented to enable any person skilled in the art to make and use the invention. Descriptions of specific applications are provided only as examples. Various modifications to the preferred embodiment will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the invention. Thus, the present invention is not intended to be limited to the embodiment shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.
• the first system 18 includes a set of k ports 20 each inputting/outputting m-bit data words in n-word bursts, an interconnection matrix circuit 22, a set of m memory access buffers 24, and a shared memory 26.
• a port serves as a two-way digital path on which digital information can be transferred to or from external circuitry such as a data bus. Port structures are well known to those skilled in the art and need not be described herein. Specific regions within the shared memory 26, indicated by dashed lines, are reserved for subsets of the data temporarily stored in the buffers 24.
• the ports 20 transfer binary data from individual external devices (not shown) connected thereto. These ports 20 provide the received binary data to the interconnection matrix 22, which distributes the data transferred through the ports among the memory access buffers 24. In the present embodiment, the distribution is accomplished such that each memory access buffer 24 receives a subset of the data transferred by each of the ports. In the present embodiment, each buffer 24 can transfer in parallel to memory 26 all of the data received by the buffer from an individual port. Moreover, all of the parallel transfers of data received from such an individual port can occur during a single memory access cycle.
• the memory read operation is analogous with the steps of the write operation, but reversed. That is, the bits for n m-bit words are transferred from the shared memory and are distributed among the memory access buffers 24.
• the interconnection matrix 22 then provides the distributed bits to a single port 20 through which a burst comprising n m-bit words is transferred to an external device (not shown) .
• Each memory access buffer 24 is dedicated to storing a specific bit position for every data word transferred through any of the ports. Data words may contain data and parity information.
• the total number of memory access buffers is equal to the total number of bits per word (m) , thus allowing each buffer to be responsible for a single bit position in every word.
• memory access buffer 24-1 stores bit 1 (Bl) of each word transferred through any of the ports 20-1 to 20-k; memory access buffer 24-2 stores bit 2 (B2) of each word transferred through any of ports 20-1 to 20-k; etc.
• each memory access buffer 24-1 through 24-k is connected to the shared memory 26 by a set of n data lines 28-1 through 28-k.
• the m-subsets of different order bits can be simultaneously transferred between the memory 26 and the buffers 24.
• there are n-bits for each of the m-subsets that is, one bit for each of the n words in an n-word burst.
• n-bits per burst there are n-bits per burst of order Bl, n-bits per burst of order B2, ..., and n-bits per burst of order B .
• All n-bits of a prescribed order can be simultaneously provided to the memory 26 on the n lines connected to a buffer assigned to store the bits of that order. For example, all n of the Bl bits are provided on the n lines connected to buffer 24-1. This means that the buffers can transfer n words at a time to or from an addressed location of memory. As explained below, all of these transferred words would have originated at or been targeted to the same external device.
• Each port 20 transfers data in a prescribed format between the interconnect matrix 22 and external circuitry (not shown) .
• a "port burst" shall mean a data burst transferred through a single port in either direction to or from the external circuitry.
• m-bit data words may be presented by a port to the interconnect matrix 22 for transfer to the buffers 24.
• m-bit data words may be presented to such a port by the interconnect matrix 22 for transfer to the external circuitry.
• the data word format involves data words with bits Bl through Bm presented in a prescribed order.
• the interconnect matrix distributes the bits as described above.
• the interconnect matrix circuit 22 can be implemented using a printed circuit board (PCB) , wire wrap or soldered wires.
• the interconnect matrix provides the connections between ports and buffers.
• each Bl in each word transferred through port 20-1 is connected by the matrix 22 to a storage element of buffer 24-1 associated with port 20-1;
• each Bl in each word transferred through port 20-2 is connected by the matrix 22 to a storage element of buffer 24-1 associated with port 20-2;
• each Bl in each word transferred through port 20-k is connected by the matrix 22 to a storage element of buffer 24-1 associated with port 20-k.
• the memory access buffers can be implemented using either standard or custom logic.
• FIG. 6-9 illustrate and explain the operation of the memory access buffers 24 and a representative dual register pair 34 of one of the memory access buffers 24.
• the illustrative block diagram of Figure 6 shows the memory access buffers 24, control logic 29, serial input/output lines 30 connecting the buffers 24 to an interconnect matrix (not shown) and a n-bit parallel input/output bus 32.
• the control logic 29 controls serial I/O on lines 30 and parallel I/O on bus 32. The operation of the control logic will be explained with reference to the timing diagram of Figure 8.
• each memory access buffer 24 includes k dual register pairs like the one shown in Figure 7 for a total of 2k registers per buffer 24.
• Each register pair in each buffer is associated with one of the ports.
• Each register pair is dedicated to storing all bits in a prescribed location (order) in every data word transferred to or from the port associated with that register pair. That is, each respective dual register pair of a respective buffer stores and transfers all of the same order bits from each data word transferred through a respective port.
• dual register pair R ⁇ receives and stores the first (in order) bit Bl of each data word transferred through port Pi (not shown).
• dual register pair Rj 2 receives and stores the second (in order) bit B2 of each word transferred through port Pj.
• dual register pair Ri m receives and stores the (in order) bit B m of each word transferred through port Pj.
• all Bis transferred through port Pj represent a subset of the data transferred through that port.
• all B2s represent another subset as do all B m s, for example.
• the dual register pair 34 includes a shift-in register 36 and a shift-out register 38.
• the shift-in register 36 first stores and then asserts in parallel n bits of data onto the memory bus 32 to be written into the shared memory 26.
• the shift-out register reads in parallel and stores n bits of data from the memory bus 32 which have been read "out" of the shared memory 26.
• the data stored in the shift-in register 36 is serially shifted from the interconnect matrix 22 into the shift-in register 36; and from there, it is asserted in parallel onto the bus 32 to be written into the memory 26 as described above.
• the data stored in the shift-out register 38 is read in parallel from the bus 32 into the shift-out register after it has been read from the memory 26; and from there, it is serially shifted from the shift-out register to the interconnect matrix 22.
• Output enable buffer 40 controls the serial transfer of data from the shift-out register 38 to the interconnect matrix 22.
• FIG 8 there is shown a timing diagram for the memory access buffers of Figures 4-6.
• memory access alternates between 32 memory read cycles followed by 32 memory write cycles.
• each port has a clock cycle during which data transferred through that port can be written to memory 26. Consecutive ports-' data are written on consecutive clock cycles, which are the respective write "time slots" for the respective ports.
• each port can begin transferring data to the memory access buffers thirty-two clock cycles before its time slot, so that there is sufficient time to transfer all thirty-two words of a burst received by a port to the buffer assigned to the port before the arrival of the port's time slot.
• Port 20-1 Data Write Cycle For example, during each Port 20-1 Data Write Cycle shown in Figure 8 all of the bits in a first word transferred through Port 20-1 are distributed by the interconnect matrix 22 among the assigned, dual port register pairs of the memory access buffers 24. For example, assuming that there are thirty- two words per burst and m bits per word, then during the first Port 20-1 Data Write Cycle, (wl.l) bit 1 (Bl) of word 1 (Wl) transferred through Port 20-1 is serially written to a prescribed register pair in buffer 24-1; B2 of Wl is serially written to a prescribed register pair in buffer 24-2; B3 of Wl is serially written to a register pair in buffer 24-3; etc. Bm of Wl is serially written to a register pair in buffer 24-m.
• Bl of W32 transferred through port 20-1 is serially written to the same register pair of port 24-1 as was Bl of Wl transferred through port 20-1.
• B6 of W3 transferred through port 20-1 is serially written to the same register pair in memory access buffer 24-6 (not shown) as was B6 of Wl transferred through port 20-1.
• rl.C is the read "time slot" for port 20-1.
• r31.C represents the read time slot for port 20-31.
• a shift-out register in buffer 24-1 receives in parallel all Bis of the thirty-two words read in parallel from the memory 26.
• a shift-out register in buffer 24-18 receives in parallel all B18s of the thirty-two words read in parallel from the memory 26.
• the interconnect matrix distributes the data word bits among multiple buffers so that each buffer only stores a subset of each word to be stored.
• each buffer stores only bits of a prescribed order.
• each buffer need only provide to the bus 32 a subset of all of the data to be simultaneously transferred to memory.
• the interconnect matrix recombines the bits distributed among multiple buffers so that they are outputted as a series (or burst) of complete words.
• the entire data to be transferred out through a port is outputted in parallel from the memory and is inputted to the buffers.
• each buffer only receives a subset of that entire data.
• the interconnect matrix 22 recombines the subsets into a burst of data words.
• the illustrative timing diagram of Figure 9 shows the operation of the dual register pair of Figure 7. During the P.WRITE pulse, data that has been read from the shared memory 26 during an (rX.c) Memory Data Cycle is written in parallel into the shift-out register 38.
• each SHIFT-OUT pulse a single bit is shifted-out from the shift-out register to the interconnect matrix 22 for transfer to a respective port.
• each SHIFT-OUT pulse corresponds to an rl.X pulse in Figure 8.
• each SHIFT-IN pulse a single bit of data is shifted in to the shift-in register.
• each SHIFT-IN pulse corresponds to an wl.X pulse in Figure 8.
• P.READ pulse all of the data that has been shifted in to the shift-in register can be read in parallel to be written to the shared memory 26 during a wl.C cycle.
• the shared memory 26 can be a standard random access memory (RAM) configuration with a memory width of (n x m) .
• the memory is able to transfer (n x m) bits of data to or from the memory access buffers 24 simultaneously, and is able to store all (n x m) bits in a single addressed location of memory, as depicted in Figure 5.
• all of the bits representing the n words from or to a specific port 20 can be readily stored as a line of the shared memory 26.
• time slots are preassigned. However, time slots could be arbitrated based on priorities. Moreover, since in the current embodiment each of the k ports 20 requires a single clock cycle time slot to communicate with the shared memory 26, and each port requires n clock cycles prior to that time slot to transfer an entire n-word data burst to or from the memory access buffers 24, it is efficient to set the number of words per burst (n) equal to the number of ports (k) , thereby providing a smooth, cyclical process for transferring data without bottlenecks or idle times. The relationship between the number of ports and words per burst can change, however, without departing from the invention.
• FIG. 10 is a block diagram of 32-port Asynchronous Transfer Mode (ATM) switch in accordance with the present invention.
• ATM is a payload multiplexing technique for information transfer using fixed-size packets, called cells.
• an ATM cell is 53-bytes long and consists of a 5-byte header which carries the routing information, followed by a 48-byte information field (payload) .
• the payload of each ATM cell entering the switch is placed in a specific location in the shared memory.
• 384 is also equal to (12 x 32) ; that is, a cell is transferred in a 32-word burst of 12-bit words.
• the ATM switch routes each received cell on a port to a destination port according to routing information that is included in each such cell. More particularly, a cell is transferred from a port and stored in shared memory. Then it is retrieved from the shared memory and is transferred to a destination port indicated in the cell. In this manner, data can be switched between ports.
• the operation of the control memory and the switch controller will be understood by those skilled in the art, form no part of the invention and need not be described herein.

Landscapes

• Engineering & Computer Science (AREA)
• Theoretical Computer Science (AREA)
• Physics & Mathematics (AREA)
• General Engineering & Computer Science (AREA)
• General Physics & Mathematics (AREA)
• Signal Processing (AREA)
• Computer Networks & Wireless Communication (AREA)
• Static Random-Access Memory (AREA)
• Dram (AREA)
• Data Exchanges In Wide-Area Networks (AREA)
• Information Transfer Systems (AREA)
• Multi Processors (AREA)
• Use Of Switch Circuits For Exchanges And Methods Of Control Of Multiplex Exchanges (AREA)
• Time-Division Multiplex Systems (AREA)
• Communication Control (AREA)

Applications Claiming Priority (3)

Publications (2)

Family

ID=22329660

Family Applications (1)

Country Status (9)

Families Citing this family (44)

Family Cites Families (8)

• 1993
  • 1993-08-19 US US08/109,805 patent/US5440523A/en not_active Expired - Lifetime
• 1994
  • 1994-08-17 AT AT94925950T patent/ATE182700T1/de not_active IP Right Cessation
  • 1994-08-17 AU AU76000/94A patent/AU682211B2/en not_active Expired
  • 1994-08-17 JP JP50719295A patent/JP3241045B2/ja not_active Expired - Lifetime
  • 1994-08-17 EP EP94925950A patent/EP0714534B1/de not_active Expired - Lifetime
  • 1994-08-17 DE DE69419760T patent/DE69419760T2/de not_active Expired - Lifetime
  • 1994-08-17 KR KR1019960700802A patent/KR100303574B1/ko not_active IP Right Cessation
  • 1994-08-17 WO PCT/US1994/009364 patent/WO1995005635A1/en active IP Right Grant
  • 1994-08-17 CA CA002168666A patent/CA2168666C/en not_active Expired - Lifetime

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events